Salt water pools and spas have become increasingly popular over the last several years. Chlorine generating salt water pools and spas are the most common and utilize systems that transform salt in the water (NaCl) to pure Chlorine (Cl) through electrolysis. In water, this quickly forms hypochlorous acid (HClO) and sodium hypochlorite (NaClO) which function as sanitation byproducts. After reacting with the contaminants in the water, these sanitation byproducts revert back to salt. The salt is then converted to chlorine again through electrolysis, and the process continues to repeat itself. This largely eliminates the need for the addition of outside sanitizers. These types of generators are installed with open loop control systems and the run time for the generator is usually set manually.
Non-salt water pools and spas may use chemical feed systems to sanitize the water in the pool or spa. These systems may be automatic or manual and, like the chlorine generator described above, they are typically installed with open loop systems where the chemical feed or sanitizer generator are set manually.
Manually setting the run time for the generator in a salt water pool or spa, or for the chemical feed or sanitizer systems in a non-salt water pool or spa, is effective provided that the sanitation demand on the system is constant. If the load is too high, the system will not generate enough sanitizer, resulting in under sanitation. In these cases, unhealthy organic build up or microbial life may develop. Alternatively, if the load is too light, extra chlorine or extra sanitizer may be generated resulting in irritation to bathers, equipment corrosion, and reduced generator cell life or reduced equipment life.
Over sanitation and under sanitation are particularly problematic in spa sanitizer systems, especially the newly developed spa sanitizer systems for salt water spas. Unlike swimming pools, many spas sit idle for long periods of time. They are generally covered and often have sophisticated filtration and sanitation systems. In these cases, it is possible that a sanitizer or a chlorine/bromine generator (in the case of salt water spas) set for one type of use one week may produce far too much sanitizer the next week when the spa goes unused and remains covered. The result can be severe corrosion of internal components and/or external decorative stainless jet trim, and severe deterioration of spa pillows, spa covers, and even jet seal O-rings.
The simplest way to overcome these problems associated with over sanitation is to include feedback to eliminate over-sanitation and over-chlorination. On the most popular spa systems available today, this is done by a timer that shuts down the system and forces the user (via indicator lights on the spa) to test the water and reset use parameters on the control system. This produces a somewhat modified open loop system. An ideal system would actually analyze the water and determine exactly how much sanitizer or chlorine is needed for proper sanitation, and how much will result in over sanitation or chlorination. From a practical standpoint, this has been historically difficult and expensive to implement on a consumer-level scale.
A more practical solution is to use an analog to proper sanitation—something that is readily (and inexpensively) measured. Fortunately, anyone who has owned a spa knows that the most common way to determine whether or not the water needs attention is simply by looking at it—i.e. by checking the clarity or opacity of the water. Accordingly, there is a need for a simple and inexpensive system and apparatus that can measure the water clarity or opacity in a pool or spa (or any other body of water) which can be easily incorporated into, and/or associated with, an existing water treatment system that already functions with the pool or spa (or any other body of water).